Hi, was most likely an air lock in the main heat exchanger of your boiler. Can happen if you don't bleed system of air correctly from bottom up (i.e. downstairs first) or just because of system design sometimes. The boiler would have cut out due to overheating from lack of water or bad circulation. Open all valves fully, put any diverter valves into the open position, fill and patiently bleed bottom up. When you refilled the system with water did you also add some more inhbitor? (protects rads from rusting and causing sludge build up)
Phil, PDC Plumbing and Heating (ex vaillant/glow-worm engineer), May 2011